Torus windings having asymmetric magnet coils

ABSTRACT

For toroidal devices, magnet coils are provided that are not axisymmetrical about their central axes. The coils have a winding cross section which, on the side nearest the torus axis, is compact and carries a higher current density, while its opposite side is expanded and carries a lower current density. The new coil designs provide coil shapes that permit construction of the individual magnet coils with an appreciable reduction of power while permitting adequate access between the coils of the torus.

States atent [191 [111 3,859,615 Luton, Jr. et al. Jan. 7, 1975 [54] TORUS WINDINGS HAVING ASYMMETRIC 3,088,894 5/1963 Koenig 176/9 X MAGNET COILS FOREIGN PATENTS OR APPLICATIONS [75] Inventors: James N. Luton, Jr.; Wilhelm F.

Gauster both of Oak g Robert 945,712 7/1949 Germany 336/229 L. Brown, Kingston, all of Tenn. Primary Examiner-Thomas J. Kozma [73] Asslgnee' gif gg g ig f zzs i zz Attorney, Agent, or Firm-John A. Horan; David S.

Atomic Energy Commission, Zachry; Lows Deckelman Washington, DC.

[22] Filed: July 30, 1973 [57] ABSTRACT [21] Appl. No.: 383,858 For toroidal devices, magnet coils are provided that are not axisymmetrical about their central axes. The [52] U S Cl 336/225 176/3 313/161 coils have a winding cross section which, on the side 3l3/23l 336/229 nearest the torus axis, is compact and carries a higher [51] Int Cl m 27/28 current density, while its opposite side is expanded [58] Fieid 225 and carries a lower current density. The new coil del76/3 5 9' 231 3l5/l i ll signs provide coil shapes that permit construction of the individual magnet coils with an appreciable reduc- [56] References Cited tion of power while permitting adequate access between the coils of the torus. UNITED STATES PATENTS 2,709,791 5/1955 Anderson, Jr. 336/229 X 7 Claims, 9 Drawing Figures lei lei M t e 1 e1 PATENTEDMN 1191s saw 1 or 2 PRIOR ART PRIOR ART PATENTEDMN Hm SHEETZUF 2 TORUS WINDINGS HAVING ASYMMETRIC MAGNET COILS BACKGROUND OF THE INVENTION This invention was made in the course of, .or under, a contract with the US. Atomic Energy Commission.

In a toroidal CTR experimental device such as the ORMAK device described in Report ORNL4793, pp. 18-27, dated August 1972, the field is obtained by a plurality of symmetrical copper coils encompassing the torus of the device. In order to substantially increase the magnitude of the magnetic field for such a device, which is desired in the near future, the field increase would correspond to about four times the power if the same winding volume were to be used. Alternatively, a sizable increase of winding volume in the usual symmetrical design in order to use the existing power is not feasible because of space restrictions toward the main axis of the torus.

Another possible solution for increasing the field without increasing the power is the use of wedgeshaped coils which provide a larger winding space without going beyond the radial confines of the existing magnet windings. Such coils are employed in the MIT Alcator machine which is described in an article published in Scientific American 227, pp. 65-75, July 1971, entitled The Tokamak Approach in Fusion Research, by B. Coppi and J. Remi; and similar coils are discussed in detail in a German paper by B. Oswald, IPP 4/96, Max Planck Institut fur Plasmaphysik, November 1971. However, the wedge-ahaped coils eliminate most of the space between coils resulting in poor accessibility for diagnostics and, in the present OR- MAK, for the planned particle injection apparatus.

Thus, there exists a need to provide a magnetic field producing system for a torus wherein the field can be increased without an appreciable power increase and without requiring more space toward the main axis of the torus while at the same time providing sufficient space for diagnostics and particle injection. The present invention was conceived to meet this need in a manner to be described hereinafter.

SUMMARY OF THE INVENTION It is the object of the present invention to provide an improved magnetic field producing system for a torus wherein a substantially larger field may be produced without an appreciable power increase and without requiring more space toward the main axis of the torus and providing adequate access for diagnostics and particle injection.

The above object has been accomplished in the present invention by providing a plurality of magnet coils encompassing a torus plasma containment chamber wherin each individual coil is not axisymmetric when viewed from the mid-circuit line but has a winding cross section which, on the side nearest the torus axis, is compact and carries a higher current density while in other areas is expanded and carries a lower current density. Magnet coils constructed in this manner can produce a doubling of the field without appreciable power increase and without requiring more space toward the main axis of the torus when compared with conventional symmetrical coils.

BRIEF DECRIPTION OF THE DRAWINGS FIG. la is a partial cross sectional view of the conventional prior art circular magnet coils of a torus device taken at the midplane.

FIG. 1b is a midplane, partial cross sectional view of a torus having conventional wedge-shaped magnet coils.

FIG. 2 is an illustration showing how a magnet coil of the present invention would replace a conventional circular coil (conventional axisymimetrical coil shown dotted).

FIG. 3a is a midplane, partial cross sectional view of a torus constructed with one type of coils of the present invention.

FIG. 3b is a midplane, partial cross sectional view of a torus constructed with an alternate embodiment of the present invention. FIGS. 4a, 4b, and 4c show cross sectional views taken on a plane through the torus major axis of three versions of the present invention FIG. 5 is a sectional, cut away, isometric view of one of the coils illustrated in FIG. 3a and in FIG. 4a of the drawings DESCRIPTION OF THE PREFERRED EMBODIMENTS The toroidal, or main, magnetic field for the ORMAK device, mentioned hereinabove, is obtained by means of 56 copper coils operated in a pulsed mode at cryogenic temperatures and powered from four generators. As shown in FIG. 1a, each of these coils is an individual circular coil that is perfectly symmetrical in cross section; that is, each coil is circular about the torus mid-circuit line. The mid-circuit line (minor axis of the torus) is defined by the radius line r extending from the torus major axis.

Recently it was desired that the magnet coils of the ORMAK be modified to produce a 50 KG field, an increase of about percent. Normally, the field in crease would correspond to about four times the power if the same winding volume were to be used. Alternatively, a sizable increase of the winding volume in the usual symmetrical design in order to use the existing power is not feasible because of space restrictions toward the main axis of the torus.

The use of wedge-shaped coils used in the prior art MIT Alcator machine is illustrated in FIG. lb of the drawings. Such coils are not suitable for the ORMAK device for the reasons given hereinabove.

The present invention consists of several embodiments of pulsed magnet coils, all of which share one common novel characteristic: an individual coil is not axisymmetric when viewed from the mid-circuit line, but has a winding cross section which, on the side nearest the torus axis, is compact and carries a higher current density while in other areas is expanded and carries a lower current density.

At the outset, it is important to point out a known but hitherto seldom applied relationship from the field of magnetics. For tori composed of a large number of coils such that the flux leakage out the gaps between coils is insignificant, the following can be proven: Every turn that encircles the minor bore (region defined by r of the torus is equally valuable and neither the strength nor the shape of the field in the bore is influenced by whether the individual turns are circular or distorted. The present invention uses this fact to save power by using large winding volumes in areas thatdo not interfere with space requirements.

A typical configuratoin of the present invention, when applied to the ORMAK device, would be as shown in FIG. 2. In that figure, the major radius r minor radius r and the original symmetric coil (dotted line) are indicated. The asymmetric coil would replace the concentric coil in the manner shown. Where the previous coil had consisted of 12 turns of copper conductor, the new coil will be made up of 24 turns to provide twice the field with no power increase. Viewed in cross section from outside the torus midplane (FIG. 3a), the coils are positioned as in FIG. la, but the expansion in the redially outward direction can be seen and the coils have a constant width. There is no closer approach to the major axis and the necessary accessibility between coils remains undisturbed.

The new coils are built with an expansion in the vertical and radially outward directions, as can be seen in FIG. 2, sufficient to reduce the total coil resistance to about one-fourth and thereby, using the existing power supply, twice the current flows through the coil windings creating twice the magnetic field. FIG. 3b shows that still further decreases in the coil resistance can be achieved if toward the torus outer periphery the width of the coils is moderately increased to such an extent that sufficient free space is still available between coils.

FIGS. 4a, 4b, and 4c illustrate three alternate forms in which the asymmetric coil of the present invention can be wound. The basic coil shape is referred to in FIG. 4a as a circular eccentric coil. The windings within this coil are on successively larger radii (r to r,) from successive centers along the line -0. Spacer material consisting of additional conducting (copper) pieces 2 as shown in FIG. 5 fills the respective spaces between turns of the winding in the expanded portions of the winding. In FIG. 5, each of the turns 1 is provided with an upturned portion 1', only one such portion being shown for the sake of clarity, wherein each of the turns may be coupled to a suitable and conventional power supply, not shown. In FIG. 4b, the coil is wound as a circular coil everywhere except at the one flat end where the conductors are arranged approximately parallel. FIG. 4c is a coil having a still different asymmetrical shape. According to the present invention, the coil of FIG. 4c, like the other embodiments, would be wound with multiple turns of the necessary winding shapes. It should be noted that the winding space toward the torus axis, designated as a, is unchanged in all of the embodiments of FIGS. 4a, 4b, and 4c Construction details of the eccentric coils described above are based on conventional techniques. It is always necessary to provide conducting material (spacers) in the nonuniform gaps in the expanded portions of the coil between the windings (for the case where the windings are made of uniform hollow copper conductors). These conducting spacers are usually copper pieces that are soldered or otherwise joined to one winding of the hollow conductor and insulated from the adjacent winding. This enables the added conductor material to become part of each turn of the coil.

In an alternate method of construction, a copper plate in the desired asymmetric shape is sawed into the proper number of turns. A groove for receiving a uniform hollow copper conductor is milled in each turn of the plate. After the conductor has been soldered in place, the plate is rotated 180 about its horizontal symmetry axis and stacked with another plate. This leaves two ends of conductor crossing each other inside the bore that are joined to become the crossover. The other conductor ends on the outside of the coil serve for connection to the power supply.

The coil designs described hereinabove when utilized to provide a magnetic field for the torus of a toroidaltype thermonuclear reactor are adapted to be connected to a conventional power supply, thereby supplying a plasma confining magnetic field for the torus. The present invention is applicable to all toroidal devices, whether working at room temperature or cryogenically, whether d.c. or pulsed. Toroidal magnetic fields are of increasing importance in thermonuclear research. The modified ORMAK may be expected to employ at least one and maybe more of the coil designs of the present invention. The asymmetric designs have as their principal advantage provision for power optimization for high fields while maintaining adequate free space in experimental toroids for diagnostics and injection apparatus. The new designs should be equally applicable to existing Tokamak machines and other toroidal devices that may be built in the future.

This invention has been described by way of illustration rather than by limitation and it should be apparent that it is equally applicable'in fields other than those described.

What is claimed is:

1. An improved magnetic field producing system for providing the toroidal fields of an experimental thermonuclear device, comprising a plurality of asymmetric coils arranged in the form of torus, each of said coils being provided with a winding cross section which has the turns thereof compact on the side nearest the torus main axis and adapted to carry a higher current density while in other areas said winding cross section is expanded in the outward directions, said other areas adapted to carry a lower current density.

2. The system set forth in claim 1, wherein there are provided variable spaces between the turns of each of said coils in the expanded portion of said winding cross section, and spacer material consisting of additional conducting pieces filling the respective said variable spaces between the turns of the winding and forming a part thereof, said coils adapted to be connected to a power supply thereby supplying a plasma confining magnetic field for said torus.

3. The system set forth in claim 2, wherein each'of said coils has a constant width.

4. The system set forth in claim 2, wherein each of said coils has a variable width toward the outer periphery thereof while still providing diagnostic access bwtween respective coils of said system.

5. the system set forth in claim 2, wherein each of said coils is a circular eccentric coil.

6. The system set forth in claim 2, wherein each of said coils is a circular concentric coil except for a flat end toward the torus main axis.

7. The system set forth in claim 2, wherein each of said coils is a circular concentric coil except for a first flat end toward the torus main axis and a second flat end opposite to said first flat end, said second flat end extending radially further from the center of said coil than said first flat end. 

1. An improved magnetic field producing system for providing the toroidal fields of an experimental thermonuclear device, comprising a plurality of asymmetric coils arranged in the form of torus, each of said coils being provided with a winding cross section which has the turns thereof compact on the side nearest the torus main axis and adapted to carry a higher current density while in other areas said winding cross section is expanded in the outward directions, said other areas adapted to carry a lower current density.
 2. The system set forth in claim 1, wherein there are provided variable spaces between the turns of each of said coils in the expanded portion of said winding cross section, and spacer material consisting of additional conducting pieces filling the respective said variable spaces between the turns of the winding and forming a part thereof, said coils adapted to be connected to a power supply thereby supplying a plasma confining magnetic field for said torus.
 3. The system set forth in claim 2, wherein each of said coils has a constant width.
 4. The system set forth in claim 2, wherein each of said coils has a variable width toward the outer periphery thereof while still providing diagnostic access bwtween respective coils of said system.
 5. the system set forth in claim 2, wherein each of said coils is a circular eccentric coil.
 6. The system set forth in claim 2, wherein each of said coils is a circular concentric coil except for a flat end toward the torus main axis.
 7. The system set forth in claim 2, wherein each of said coils is a circular concentric coil except for a first flat end toward the torus main axis and a second flat end opposite to said first flat end, said second flat end extending radially further from the center of said coil than said first flat end. 